Causes

Congenital

Birth Trauma: several factors during the birth of a child may lead to facial nerve injury and associated paralysis. These include instrumentation (the use of forceps during the delivery), birth weight over 3.5 kg (7.7 lb), and first pregnancy. A contributing factor may be compression molding of the fetus while passing through the birth canal. In this setting, the facial nerve undergoes stretch injury and requires time to regenerate. The overall prognosis is excellent, with up to 90% of children achieving complete recovery of their facial nerve function without surgical or medical intervention1. In rare instances where transection injury is highly suspected, surgical exploration may be warranted.

Mobius Syndrome: this syndrome was described in the 19th century and is characterized by concomitant facial nerve and abducens nerve palsies2. Clinically, patients are unable to move their face and have extreme difficulty expressing emotion. This may be accompanied by oral incompetence, drooling, low self-esteem, and social isolation - all of which add to the challenges of those suffering from this condition. In this patient group, free muscle transfer has been successfully utilized for rehabilitation of facial movement3,4. Ideally, such intervention would be performed prior to school entry, in an attempt to avoid psychological trauma from peer ridicule during early formative years.

Melkersson-Rosenthal Syndrome: recurrent facial paralysis, facial swelling, and tongue fissures characterize this rare syndrome. While typical care of recurrent flare-ups includes steroid and anti-inflammatory medications, controversy remains over the management and prevention of facial palsy. Isolated case reports describing facial nerve decompression5 (drilling out its bony confines to prevent nerve pressure during bouts of swelling) suggest that long-term resolution of facial nerve dysfunction is possible with this more aggressive approach.

Hemifacial Microsomia: represents a spectrum of congenital facial anomalies, arising due to lack of development of one side of the face. This syndrome is marked by hemifacial soft tissue deficiency and poor development of the lower jaw, maxilla, and external ear. In cases of accompanying facial weakness or paralysis, reconstructive surgery can be planned together with craniofacial repair, directed at correcting jaw and ear abnormalities. Facial symmetry and smile restoration can be especially effective with free muscle transfer, as it provides a secondary benefit of facial augmentation6.

Infectious

Bell's Palsy: this condition is also known as idiopathic (cause unknown) facial paralysis and represents its most common cause. Recent evidence suggests that herpes simplex virus is the most likely agent behind Bell's palsy7. The incidence of this condition approaches 30 per 100,000 people. Typically, the onset of paralysis occurs over a period of 24 - 72 hours and may be accompanied by other symptoms, such as pain around the ear, decreased taste, and diminished hearing on the affected side.

While the overwhelming majority of patients recover their facial nerve function, a small minority retains a deficit, which is typically complicated by aberrant facial movements (synkinesis). Steroids and anti-viral medicines have been found helpful in improving functional recovery of the facial nerve in the acute stages of the disease8,9. In select instances, where electrical activity of the nerve is severely depressed, surgical decompression of the nerve's bony channel has been shown to be beneficial10. In those with poor recovery and synkinesis, chemodenervation (paralysis) with Botox and intensive physical therapy offer a promising rehabilitative option.

Ramsey-Hunt Syndrome: is caused by reactivation of Varicella Zoster virus (a herpes family virus) in the facial nerve, leading to facial paralysis on the involved side. This is accompanied by formation of vesicles and pain in the ear (zoster oticus), which clinically distinguishes this condition from Bell's palsy. Other symptoms, such as hearing loss, tinnitus (noise in the ear), vertigo (imbalance), nausea, and vomiting may be present as well. These are thought to arise from irritation of the hearing and balance nerves, which are situated adjacent to the inflamed facial nerve in the temporal bone.

While no randomized studies exist on the treatment of this infrequent condition, a combination of steroids, antivirals, and pain medications are used to control inflammatory injury of the facial nerve11,12,13. This regimen is based on the experience with Bell's palsy (steroids) as well as treatment of zoster infections in other parts of the body (with anti-viral medications). Prognosis for facial nerve recovery is poor in Ramsey Hunt syndrome, with chronic neuralgia (pain) commonly persisting following the resolution of infection.

Otitis Media / Mastoiditis: is an acute infection of the middle ear and mastoid (bone behind the ear), which in rare cases (less than 1%) may result in facial nerve paralysis. Swelling around the nerve and toxic substances released by bacteria are thought to be causative factors behind facial nerve involvement.

Successful treatment consists of prompt recognition and eradication of infection. This includes broad- spectrum antibiotics and incision of the tympanic membrane with placement of a ventilation tube, allowing to obtain bacterial specimen for culture. A mastoidectomy (removal of infection in the adjacent mastoid bone) may be performed in select cases of associated mastoiditis. Prognosis for complete facial nerve recovery is excellent with the above interventions14, 15.

Cholesteatoma: is a slow-growing skin cyst that over time causes destruction in the ear by exerting pressure on surrounding structures and causing flare-ups of chronic infection. The incidence of facial paralysis in a setting of cholesteatoma approaches 3%16. Prompt recognition of this disease process and surgical eradication are critical in successfully releasing pressure from the facial nerve and removing the source of chronic infection and inflammation.

Poor prognostic factors for recovery include extension of cholesteatoma into the petrous apex (deep portion of the temporal bone) and delayed surgical treatment17. Patients who undergo early intervention are more likely to recover their facial nerve function completely.

Lyme Disease: is caused by Borrelia Burgdorferi - a bacterium transmitted to humans through the bite of infected ticks. Typical symptoms and signs in acute stages of Lyme disease include headache, weakness, fever, and erythema chronicum migrans (a characteristic target-shaped rash that develops at the site of tick bite).

While the incidence of accompanying facial paralysis reaches 11%, it completely resolves in 99.2%18. A high index of suspicion for Lyme disease should arise in a patient presenting with a recent history of tick bites, during summer months, and in endemic areas (the national risk map is available on the CDC website http://www.cdc.gov/ncidod/dvbid/lyme/riskmap.htm). Lyme titers should be obtained for confirmation and antibiotic therapy instituted, following published guidelines by the infectious disease society of America19.

Other: A number of additional infectious processes can impair facial nerve function and include diseases such as HIV (human immunodeficiency virus), TB (tuberculosis), infectious mononucleosis, and other20,21,22,23. These conditions typically have other associated symptoms in affected individuals and require a high index of suspicion to make the diagnosis. Previous history and risk factors of exposure influence the decision to pursue these diagnostic possibilities in a setting of facial paralysis.

The mainstay of management is targeted medical therapy, unless associated mastoiditis (infection involving the mastoid bone, through which the facial nerve passes) is identified on work-up. In this instance, mastoidectomy (surgical removal of infected mastoid bone) should be performed to control the infection and swelling around the facial nerve.

Systemic & Neurologic

Conditions in this category include autoimmune diseases, diabetes, sarcoidosis, Guillain-Barre syndrome, multiple sclerosis, and other. Infrequently, these can present with isolated facial paralysis24,25,26,27. Correct diagnosis and prompt medical intervention form the initial treatment strategy, with anticipated recovery of facial movement in most cases.

Traumatic

Traumatic injuries to the head and cranium represent one of the most common causes of acquired facial paralysis. In instances of blunt trauma, in which no lacerations or fractures occur, the facial nerve retains its continuity and is expected to recover28. In a setting of suspected nerve laceration (penetrating trauma through facial skin and soft tissues), immediate surgical exploration with nerve repair is warranted. Ideally, this would take place within 3 days of injury, during which the distal portion of the facial nerve can still be stimulated and, thus, identified during surgery.

When facial trauma results in the temporal bone fracture, accompanying facial nerve injury can occur in 5-10% of cases. Full recovery is expected in those patients who experience delayed onset of facial paralysis. In contrast, approximately 40% of those with immediate onset of paralysis recover poorly29. In many cases of significant facial trauma, other concomitant acute conditions may delay examination and testing of the facial nerve. However, delayed surgical exploration, even months after the injury, can still be performed30,31,32 with reasonable success rates of functional improvement and recovery.

Iatrogenic injury to the facial nerve can occur during facial, bony, or intracranial surgery. The extent of nerve damage largely dictates the type of repair33. In severe cases, nerve repair may not be possible and other rehabilitative methods must be utilized (diagram - chronic facial paralysis).

Neoplastic

Extirpation of cancer situated in the vicinity or invading the facial nerve may require significant nerve manipulation during surgery and possibly partial or complete transection. The most common tumors affecting the facial nerve are acoustic neuroma (vestibular schwannoma), glomus, facial neuroma, and carcinoma (malignancy involving the brain, temporal bone, parotid gland, and soft tissues adjacent to the course of the facial nerve). When the facial nerve continuity is preserved during surgery, post-operative recovery is closely monitored. Stimulation of the nerve at the end of the procedure may provide useful prognostic data. Steroid medications are typically not given in this setting, as several studies have clearly shown lack of benefit34,35.

Following surgery, electromyography (EMG) can be utilized to assess re-innervation of facial musculature. Depending on the stage of recovery, as well as individual challenges and concerns, several simple procedures are considered to aid with eye closure, facial symmetry, and oral competence (diagram - intermediate facial paralysis).